In the start-up of activated carbon treatment for aqueous systems, it is typical to experience unacceptable increases in the pH and/or alkalinity of the effluent. As used herein, the term "alkalinity" shall mean the water's acid-neutralizing capacity and is defined as the sum of all titratable bases. These unacceptable levels of pH or alkalinity contents can last from several hours to several days. For example, excursions have been experienced for over 500 bed volumes. This effect has also been found for activated carbons already on-line and subjected to sudden changes in influent water chemistry (e.g. pH). When these excursions occur, the treated water does not meet the standards for distribution to the customer or discharge to the environment. This problem can lead to a significant loss in production, environmental problems, or expensive remedial actions.
The pH/alkalinity excursion phenomenon has been found to occur for various types of water treatment applications such as municipal water, industrial process water, ground water, and home water filter applications. It has been found to exist using various types of activated carbons such as those produced from bituminous, subbituminous, wood, coconut, peat feedstocks, or those which are acid-washed prior to use.
The presence of these pH/alkalinity excursions has been a recurring problem throughout the industry for many years. Notwithstanding the productivity losses associated with these excursions, little or nothing has been done to overcome or alleviate the problem. pH/alkalinity excursions have been largely tolerated because no solution was known to exist. Because of the growing concern for the environmental problems associated with these excursions as well as the economic losses, it is an object of the invention to provide a method for preventing or eliminating them. Accordingly, it is an object of the present invention to provide an oxidized activated carbon that is useful in preventing pH and alkalinity excursions in the start-up phase of aqueous adsorption systems.